Method of reducing the solution viscosity of cellulose



Patented Apr. 18, 1933 \UNITED "STATES PATENT OFFICE J. GALLAEAN, 0EPABLIN, NEW JERSEY, ASSIGNOR T0 E. I. DU PONT DE NEMOURS & COMPANY, OF'WILMING'I'dN, DELAWARE, A CORPORATION OF- DELA- a WARE METHOD OFREDUCIN G THE SOLUTION VISCOSITY OF CELLULOSE lo Drawing.

This invention relates to a method of .reducing the normal solutionviscosity of cellulose. Cellulose derivatives of solution viscositiesmuch lower than normal from cellulose of reduced solution viscosity, aresuitable for use where cellulose derivatives having subnormal solutionviscosity combined with normal film forming properties are desired. Oneof the disadvantages of cellulose derivatives for use insolutions and incoating compositions is the high solution viscosity of the productasmade bythe usual methods. This difficulty is common to all derivativesof cellulose, and has interfered with the general commercial applicationof such derivatives, especially in coating compositions such aslacquers, varnishes and the like, in which. the cellulose derivative isdissolved in a volatile $01- trade.

It has been proposed to reduce the solution viscosity of cellulose bytreating the cellulose with hydrogen chloride under conditions whichresults in the de adation of the cellulose nucleus with comp ete loss ofthe fibrous structure in the more or less powdery product. Thisloss infibrous structure is"especially disadvantageous in the nitration of thecellulose because of the mechanical difiiculties in recovering thenitratin acid mixture aforesaid manner, cannot be satisfactorilyseparated from the acid by centrifuging because the finely dividedcondition ofgthe prod- .uct permits it to escape with the nitrating liquid. Another method, known to the prior art, of producinglow solutionviscosity ni-- trocellulose is to nitrate high solution VISCOS- itycellulose and subsequently reduce the solution viscosity of thenitrocellulose by heating in water suspension under pressure. ThisApplication filed July 2, 1930. Serial 1T0. 465,454.

latter method is a relatively dangerous operation.

This invention has as an object an improved method of preparing solutionlow viscosity cellulose. A further object is the preparation of lowsolution viscosity cellulose derivative by a process which is easilycontrolled and economical.

The first object is accomplished by the following invention in whichcellulose is treated with an acid gas, preferably hydrogen chloride,under conditions which reduce the solution viscosity of the cellulosewithout substantially impairing its fibrous structure. The second objectis accomplished by treating the aforesaid cellulose of reduced solu tionviscosity with a reagent capable of forming the desired cellulosederivative.

I have found that the solution viscosity of cellulose can be effectivelyand uniforml reduced and controlled by treatments wit very smallproportions of hydrogen chloride. The following examples areillustrative of the preferred methods of carrying out the invention,although it will be understood that the invention is not limitedthereto, as other modes of procedure may be adapted within the spirit ofthe invention.

Example 1 A sample of air-dried cotton linters, which had been freedfrom waxes and other impurities by a caustic digestion, was treated 'atroom temperature for one-half hour with an amount of hydrogen chlorideequal to 0.5% b weight of the cotton. The hydrogen chlori e was vestrongly adsorbed,since no odor of it could e detected in the cottonlinters. The treated cotton linters were allowed to stand 48 hours atroom temperature. The

material was then washed to remove the hydrochloric acid and dried. Theviscosityof the resulting cellulose in cuprammonia solution was 1.207compared with wateras one. The solution viscosity of the originallinters was so high that the cellulose would not dis,- solve in thecuprammonia'solution.

The method of determining the solution' viscosity was as follows :Dudleypipettes of l 100 cc. capacity, giving 33-35 sees. for water at wereselected and is ca use the pipettes were surrounded by a water 3 jacketat 25 C. On-measuring the solution viscosity of a sample of cotton, 3.05gms. of cupric hydroxide, 2.00 gms. of cotton linters, and 225 cc. ofammonium hydroxide (Sp. gv. 0.96) at 25 C. are. introduced into an 8 oz.wide mouth bottle, thebottle is closed by means of a cork, and themixture is shaken exactly two minutes. The solution is then allowed tostand exactly one minute, after which it is drawn into the pipette andthe time of draining of 100 cc. is measured with a stop-watch. The secific solution viscosity 'culated by re erence to the draining time ofwater.

The measured or calculated amount of hyidrogen chloride gas may bepassed from any suitable source into a closed vessel, as a bell 'ar,containin the cellulose to be treated.

e amount 0 hydrogen chloride, expressed as a percentage of the weight ofthe cellulose, with which the cellulose is treated, may vary from about0.1% to about 2%. The duration of the treatment, which includes the timeduring which the cellulose with its adsorbed hydrogen chloride standsbefore the treatment is discontinued by washing or otherwise separatingthe reagent from the cellulose,

- the treatment takes place; andthe reduction in viscosity desired. Forinstance, cellulose treated with 0.1% hydro en chloride at roomtemperature, about 25 may he permitted to stand twenty-four hours ormore to obtain a desired solution viscosity, whereas onehalf hour wouldbe sufiicient time at 100 (1., for the same percentage of hydrogenchloride. A long time at 100 C. has a detrimental-action upon thecellulose. As the amount of hydrogen chloride approaches the upperlimit, the time of standing is shorter and the be no substantialimpairment of tlie fibrous structure of the cellulose. Thus with 2% ofhydrogen chloride at room temperature the cellulose should not bepermitted to stand after the gas is passed into the cellulose. It willbeseen, therefore that for a given percentage of hydrogen c oride, theamount of solution viscosity'reduction of the cellulose is regulated bythetime of treatment which in turn depends upon the temperature at whichthe treatment takes place. The hydrogen chloride treatment, however.(whethefiextnded or brief as determine by the percentage of hydrogenchloride, the solution viscosity desired and the temperature), isaccording to the resent invention,-

terminated before any su staiitial disintetion of the cellulose, orchange the.

ions structure takes place. appeardraining times ofdepends upon thepercentage of hydro-' gen chloride used; the temperature atwhichmperature lower in order that thereshall ance and physicalcharacteristics of the cellulose after the treatment is essentially thesame as before the treatment.

I have found that the. presence of moisture in the cellulose isimportant. With cellulose dried at. 100 (1., dry hydrogen chloufactureof low solution viscosity types of 1 nitrocellulose as indicated by thefollowing examples:

Ewample 2 Purified cotton .linters, characterized by a solutionviscosity of 1.80 compared to water as 1, are treated with 0.5% ride gasand allowed to standvfive hours at hydrogen chlo- 50 C: The solutionviscosity of the cellulose is thereby decreased to 1.20-1.25. Thiscotton may be ni rated with a mixed acid containing apiplroximately22.5% nitric acid and 58.5% su ic acid for 30 minutes at 40 C.

The resulting nitrocellulose contains about 11.8% nitrogen andhas asolution viscosity between 2 and3' seconds by the falling sphere method.v

, Example 3 The same type of high solution viscosity cotton linter'istreated with"1% hydrogen chloride gas for three days at 25 C. Thesolution viscosity is then about 120 and on nitratiomyields anitrocellulose of 2-3 seeondssolutlon viscosity containing 11.8%nitrogefi.

It is apparent from the examples that the exact conditions ofconcent'rationl of hydrogen chloride, time, and temperature of treat.-

ment of the cotton linters'may be varied quite widely and, provided thesolution viscosity of the cotton comes out about the same thenitrocelluloses which may be prepared from the pretreated cellulosehaveapproximately the same viscosity characteristics if the nitrati'onsare com arable.

Cellu ose which isp etreated with hydro- I en chloride gas so'tha itssolution viscosity is thereby decreased may be used advantageo ly in"the manufacture of reduced solution viscosity cellulose acetate bydirect acetylation. Under the conditions of pretreatment as hereindisclosed, it has been observed that the cellulose is rendered morereactive toward acetylating agents than an untreated cellulose. y

In addition to. the nitrocellulose and cellulose acetate, any cellulosederivative of the ester or other type can be obtained in reducedsolution viscosity form if prepared from a cellulose pretreated withhydrogen chloride gas in the manner'described. Such low solutionviscosity derivatives in many cases find application as substitutes foreither nitrocellulose or cellulose acetate.

Hydrochloric acid gas is notthe only acid which can be employed in myprocess. Other halogen acids such as hydrobromic acid or substanceswhich produce the acids in the presence of water, may he used. Where itis desired to obtain better distribution of the gas throughout thecellulose, or to prolong the time necessary to accomplish the adsorptionof the gas by the cellulose, the acid gas may be diluted by anon-reactive or inert gas, such as air or nitrogen.

My improved process for producing cellu- I lose and cellulosederivatives is easily controlled and does not require expensiveapparatus. It requires but a short amount of time to reduce the solutionviscosity of the cellulose or the derivative thereof to a requireddegree, and thus makes possible a rapid turnover which is a distinctadvantage in large scale manufacture. The fact that the fibrousstructure of the cellulose is maintained and may therefore be easilyseparated from the liqu d during centrifuging is of especial value inthe production of cellulose nitrate because of the saving effected inrecovering the nitra-ting mixture.

As many apparently widely difierent embodiments of this invention may bemade without departing from the spirit and scope reactive'ingredient,from 0.1% to 2. 0% of its weight of a hydrogen halide, and discontinuinfg the treatment efore the fibrous structure o the cellulose issubstantially impaired. In testimony whereof, I aflix m' signature.

MICHAEL J. i

thereof, it is to be understood that I do not limit myself to thespecific 'embodin uents ,thereof except as defined in the appendedclaims.

I claim: y

1. method of reducing the solution viscosityof cellulose which comprisestreating the cellulose w th a gas containing a hydro-1 gen halide as itssole reactive ingredient to reduce the solution viscosity of thecellulose, and discontinuing the treatment before the fibrous structureof the cellulose is substantially impaired.

weight of hydrogen chloride, and discontinuing the treatment before thefibrous structure of the cellulose is substantially impaired.

4. The method of reducing the solution .viscosity of cellulose whichcomprises treating the cellulose with a gas containing, as its sole

